Dual coupler device, spectrometer including the dual coupler device, and non-invasive biometric sensor including the spectrometer

ABSTRACT

Provided are a dual coupler device configured to receive lights of different polarization components, a spectrometer including the dual coupler device, and a non-invasive biometric sensor including the spectrometer. The dual coupler device may include, for example, a first coupler layer configured to receive a light of a first polarization component among incident lights. and a second coupler layer configured to receive a light of a second polarization component among the incident lights, wherein a polarization direction of the light of the first polarization component is perpendicular to a polarization direction of the light of the second polarization component. The first coupler layer and the second coupler layer may be spaced apart from each other and extended along a direction in which the light propagates in the first coupler layer and the second coupler layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2015-0024020, filed on Feb. 17, 2015 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in byreference its entirety.

BACKGROUND

1. Field

Apparatuses and methods consistent with exemplary embodiments relate todual coupler devices configured to receive lights of differentpolarization components, spectrometers including the dual couplerdevices, and non-invasive biometric sensors including the spectrometers.

2. Description of the Related Art

A non-invasive blood sugar measurement may be performed throughspectroscopic analysis of a biometric signal that is obtained whenincident light is reflected off the skin of a human subject. Withimprovements in performance of mobile apparatuses such as mobile phones,integrating a non-invasive biometric sensor into a mobile apparatus maybe attempted. To this end, a micro spectrometer may be installed in amobile apparatus.

For example, the micro spectrometer may be implemented as a linearvariable filter (LVF)-based spectrometer or a filter array-basedspectrometer. The LVF-based spectrometer may have a structure in which aspacer having a gradually changing thickness is disposed on a pluralityof photodiode pixels so that the thickness of the LVF-based spectrometervaries continuously or in steps. Respective photodiode pixels in theLVF-based spectrometer may sense lights of different wavelength bandsbecause a transmission wavelength varies depending on the thickness ofthe spacer. The filter array-based spectrometer may have a structure inwhich band-pass filters (BPFs) of different transmission bands aredisposed in respective photodiode pixels.

SUMMARY

One or more exemplary embodiments provide dual coupler devices that areused in silicon photonics-based spectrometers and are configured toreceive lights of different polarization components.

Further, one or more exemplary embodiments provide spectrometersincluding the dual coupler devices.

Further still, one or more exemplary embodiments provide non-invasivebiometric sensors including the spectrometers.

According to an aspect of an exemplary embodiment, there is provided adual coupler device including: a first coupler layer configured toreceive a light of a first polarization component among incident lights;and a second coupler layer configured to receive a light of a secondpolarization component among the incident lights, wherein a polarizationdirection of the light of the first polarization component isperpendicular to a polarization direction of the light of the secondpolarization component, and the first coupler layer and the secondcoupler layer are spaced apart from each other and extended along adirection in which the incident lights propagate in the first couplerlayer and the second coupler layer.

The first coupler layer and the second coupler layer may be parallel toeach other.

Also, the first coupler layer and the second coupler layer may bedisposed to face each other.

The dual coupler device may further include a transparent dielectriclayer in which the first coupler layer and the second coupler layer maybe buried.

The first coupler layer and the second coupler layer may have a higherrefractive index than the transparent dielectric layer.

The first coupler layer and the second coupler layer may each include agrating-type coupler having a periodic grating structure.

The periodic grating structure of the first coupler layer may beconfigured to have selectivity with respect to the light of the firstpolarization component, and the periodic grating structure of the secondcoupler layer may be configured to have selectivity with respect to thelight of the second polarization component.

The periodic grating structure of the first coupler layer may beconfigured to have selectivity with respect to a light of a firstwavelength band, and the periodic grating structure of the secondcoupler layer may be configured to have selectivity with respect to alight of a second wavelength band that overlaps at least partially withthe first wavelength band.

Herein, the first wavelength band and the second wavelength band may besubstantially identical to each other.

The dual coupler device may further include a reflector configured toreflect light, which passes through the first coupler layer and thesecond coupler layer among the incident lights, towards the firstcoupler layer and the second coupler layer.

The reflector may be disposed apart from the first coupler layer by afirst distance that creates destructive interference with the light ofthe second polarization component and constructive interference with thelight of the first polarization component in the first coupler layer.

The reflector may be disposed apart from the second coupler layer by asecond distance that creates destructive interference with the light ofthe first polarization component and constructive interference with thelight of the second polarization component in the second coupler layer.

According to an aspect of another exemplary embodiment, there isprovided a spectrometer including: a first coupler layer configured toreceive a light of a first polarization component among incident lights;a second coupler layer configured to receive a light of a secondpolarization component among the incident lights; and a photodetectorconfigured to detect the light received by each of the first couplerlayer and the second coupler layer, wherein a polarization direction ofthe light of the first polarization component is perpendicular to apolarization direction of the light of the second polarizationcomponent, and the first coupler layer and the second coupler layer arespaced apart from each other and extended along a direction in which theincident lights propagate in the first coupler layer and the secondcoupler layer.

Herein, the first coupler layer may include: a first input couplerconfigured to selectively couple the light of the first polarizationcomponent; a first waveguide along which the light of the firstpolarization component coupled by the first input coupler propagates; afirst resonator configured to resonate the light of the firstpolarization component coupled by the first input coupler; and a firstoutput coupler configured to output the light of the first polarizationcomponent resonated by the first resonator to the photodetector.

Also, the second coupler layer may include: a second input couplerconfigured to selectively couple the light of the second polarizationcomponent; a second waveguide along which the light of the secondpolarization component coupled by the second input coupler propagates; asecond resonator configured to resonate the light of the secondpolarization component coupled by the second input coupler; and a secondoutput coupler configured to output the light of the second polarizationcomponent resonated by the second resonator to the photodetector.

The first coupler layer may include at least two first resonatorsconfigured to resonate lights of different wavelengths respectively, andthe second coupler layer may include at least two second resonatorsconfigured to resonate lights of different wavelengths respectively.

One of the at least two first resonators of the first coupler layer andone of the at least two second resonators of the second coupler layermay be configured to resonate lights of substantially the samewavelength.

The first resonator of the first coupler layer and the second resonatorof the second coupler layer configured to resonate lights of the samewavelength may be disposed to face each other.

The first coupler layer may include at least two first input couplersconfigured to selectively couple lights of different wavelengthsrespectively, and the second coupler layer may include at least twosecond input couplers configured to selectively couple lights ofdifferent wavelengths respectively.

The first input coupler may be optically connected to the at least twofirst resonators, and the second input coupler may be opticallyconnected to the at least two second resonators.

The first coupler layer may include at least two first waveguidesoptically connected to the at least two first resonators respectively,and the second coupler layer may include at least two second waveguidesoptically connected to the at least two second resonators respectively.

The first output coupler and the second output coupler may be disposedrespectively at positions that do not overlap with each other in a lightpropagation direction in the first waveguide and the second waveguide.

The spectrometer may further include a first reflector disposed to facethe first input coupler and the second input coupler and configured toreflect light, which passes through the first coupler layer and thesecond coupler layer among the incident lights, towards the firstcoupler layer and the second coupler layer.

The first reflector may be disposed apart from the first coupler layerby a first distance that creates destructive interference with the lightof the second polarization component and constructive interference withthe light of the first polarization component in the first inputcoupler.

Also, the first reflector is disposed apart from the second couplerlayer by a second distance that creates destructive interference withthe light of the first polarization component and constructiveinterference with the light of the second polarization component in thesecond input coupler.

Also, the spectrometer may further include a second reflector disposedto face the first output coupler and the second output coupler andconfigured to reflect the light, which is output from the first outputcoupler and the second output coupler, to the photodetector.

According to an aspect of another exemplary embodiment, there isprovided a non-invasive biometric sensor including: a light sourceconfigured to radiate an excitation light to an object; and aspectrometer configured to measure a spectrum distribution of ascattered light generated from the object by the excitation light. Thespectrometer may include a first coupler layer configured to receive alight of a first polarization component among incident lights; a secondcoupler layer configured to receive a light of a second polarizationcomponent among the incident lights; and a photodetector configured todetect the light received by each of the first coupler layer and thesecond coupler layer, wherein a polarization direction of the light ofthe first polarization component is perpendicular to a polarizationdirection of the light of the second polarization component, and thefirst coupler layer and the second coupler layer are spaced apart fromeach other and extended along a direction in which the incident lightspropagate in the first coupler layer and the second coupler layer.

According to an aspect of another exemplary embodiment, there isprovided a spectrometer including: a first coupler layer configured toreceive light of a p-polarization component through a first inputcoupler; a second coupler layer that is configured to receive light of as-polarization component through a second input coupler and disposed tobe apart from the first coupler layer in a first direction perpendicularto a second direction in which the light of the p-polarization componentand the light of the s-polarization component propagate in the firstcoupler layer and the second coupler layer, respectively; and areflector that is disposed to be apart from the first coupler layer andthe second coupler layer in the first direction, aligned with the firstinput coupler and the second input coupler in the second direction, andconfigured to bounce off light incident from the first coupler input andthe second input coupler back to the first input coupler and the secondinput coupler.

The first coupler layer may propagate the light of the p-polarizationcomponent towards a first output coupler disposed on the first couplerlayer, the second coupler layer may propagate the light of thes-polarization component towards a second output coupler disposed on thesecond coupler layer, and the first output coupler may be disposed outof alignment with the second output coupler in the second direction.

The spectrometer of may further include another reflector that isdisposed to be apart from the first coupler layer and the second couplerlayer in the first direction and is aligned to bounce off light incidentfrom the first output coupler and the second output coupler back to thefirst output coupler and the second output coupler.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will be more apparent by describingcertain exemplary embodiments, with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic perspective view of a spectrometer according to anexemplary embodiment;

FIG. 2 is a schematic perspective view of a spectrometer according toanother exemplary embodiment;

FIG. 3 is a schematic cross-sectional view of a coupler device accordingto an exemplary embodiment;

FIG. 4 is a schematic cross-sectional view of a coupler device accordingto another exemplary embodiment;

FIG. 5 is a schematic block diagram of a non-invasive biometric sensoraccording to an exemplary embodiment;

FIG. 6 illustrates an example of an optical arrangement of thenon-invasive biometric sensor illustrated in FIG. 5;

FIG. 7 illustrates another example of the optical arrangement of thenon-invasive biometric sensor illustrated in FIG. 5; and

FIG. 8 illustrates another example of the optical arrangement of thenon-invasive biometric sensor illustrated in FIG. 5.

DETAILED DESCRIPTION

Exemplary embodiments are described in greater detail below withreference to the accompanying drawings.

In the following description, like drawing reference numerals are usedfor like elements, even in different drawings. The matters defined inthe description, such as detailed construction and elements, areprovided to assist in a comprehensive understanding of the exemplaryembodiments. However, it is apparent that the exemplary embodiments canbe practiced without those specifically defined matters. Also,well-known functions or constructions are not described in detail sincethey would obscure the description with unnecessary detail.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

Hereinafter, dual coupler devices, spectrometers including the dualcoupler devices, and non-invasive biometric sensors including thespectrometers according to exemplary embodiments will be described indetail with reference to the accompanying drawings. In the drawings, thesizes of elements may be exaggerated for clarity and convenience ofdescription. It will be understood that when a layer is referred to asbeing “on” another layer, it may be directly on the other layer, or oneor more intervening layers may also be present.

FIG. 1 is a schematic perspective view of a spectrometer according to anexemplary embodiment. Referring to FIG. 1, the spectrometer 100 mayinclude a coupler device 140 based on silicon photonics and aphotodetector 150. For example, the coupler device 140 may receive ascattered light LS from an object, divide the scattered light LSaccording to wavelengths, and provide the divided lights to thephotodetector 150. The photodetector 150 may detect the intensities of aplurality of light beams divided by the coupler device 140 according towavelengths. For example, the photodetector 150 may include a chargecoupled device (CCD) image sensor, a complementary metal oxidesemiconductor (CMOS) image sensor, or an array of photosensors. Thespectrometer 100 may analyze a spectrum distribution of the scatteredlight LS in relevant wavelength bands.

The coupler device 140 may include an input coupler 111 configured tocouple an incident light to the coupler device 140, a waveguide 112along which the light coupled by the input coupler 111 propagates, aresonator 113 configured to resonate the light coupled by the inputcoupler 111, and an output coupler 114 configured to output the lightresonated by the resonator 113 to the photodetector 150. The resonator113 may include two resonator mirrors 121 and 122 disposed in thewaveguide 112. In this structure, the light coupled by the input coupler111 may propagate along the waveguide 112. Also, the light may resonatebetween the two resonator mirrors 121 and 122 of the resonator 113, andonly the light having a resonance wavelength of the resonator 113 may beoutput from the resonator 113. The light output from the resonator 113may propagate from the coupler device 140 to the photodetector 150through the output coupler 114.

In order to divide the incident light according to wavelengths, thecoupler device 140 may include at least two input couplers 111, at leasttwo waveguides 112, at least two resonators 113, and at least two outputcouplers 114. The input couplers 111 may be configured to respectivelycouple lights of different wavelengths. For example, one of the inputcouplers 111 may be configured to selectively couple a light of a firstwavelength band λ1, and another of the input couplers 111 may beconfigured to selectively couple a light of a second wavelength band λ2.Also, the resonators 113 may be configured to respectively resonatelights of different wavelengths. For example, one of the resonators 113may be configured to resonate a light of the first wavelength band λ1,and another of the resonators 113 may be configured to resonate a lightof the second wavelength band λ2. The resonance wavelength of theresonator 113 may be adjusted by the distance between the two resonatormirrors 121 and 122. The resonator 113 may be optically connected to anyone of the input couplers 111 and resonate the light of substantiallythe same wavelength band as the selective wavelength band of the inputcoupler 111 connected thereto. For example, the input coupler 111configured to selectively couple the light of the first wavelength bandλ1 may be optically connected to the resonator 113 having a resonancewavelength of the first wavelength band λ1.

As illustrated in FIG. 1, the input couplers 111, the waveguides 112,the resonators 113, and the output couplers 114 may be disposed inparallel to each other at different positions in the widthwise directionof the coupler device 140. According to the present exemplaryembodiment, the lights of different wavelengths may be incident on thephotodetector 150 respectively from the output couplers 114 disposed atthe different positions in the widthwise direction of the coupler device140. Then, the lights of different wavelengths may be respectivelyincident on different positions of the photodetector 150. Thus, aspectrum distribution of the incident light may be analyzed by measuringthe intensities of lights respectively incident on the differentpositions of the photodetector 150.

FIG. 1 exemplarily illustrates five input couplers 111, five waveguides112, five resonators 113, and five output couplers 114. Thus, thespectrometer 100 may divide the incident light into five wavelengthbands λ1, λ2, λ3, λ4, and λ5. However, the number of input couplers 111,waveguides 112, resonators 113, or output couplers 114 illustrated inFIG. 1 is merely exemplary. For example, ten or more input couplers 111,waveguides 112, resonators 113, and output couplers 114 may be disposedto analyze desired biometric information on the basis of biometricoptical signals transmitted or scattered from a living body.

Also, although FIG. 1 illustrates that the input coupler 111, theresonator 113, and the output coupler 114 are physically connectedthrough one waveguide 112, this is merely exemplary. That is, the inputcoupler 111, the resonator 113, and the output coupler 114 may not bephysically connected through one waveguide 112, and any means may beused to transmit the light from the input coupler 111 to the resonator113 and transmit the light from the resonator 113 to the output coupler114. For example, an empty space may exist between the resonator 113 andthe output coupler 114, and the waveguide 112 may exist only partiallytherein. Thus, the input coupler 111, the waveguide 112, the resonator113, and the output coupler 114 may be optically connected although notphysically connected. Also, a light path from the input coupler 111 tothe output coupler 114 may not necessarily be a straight line.

FIG. 2 is a schematic perspective view of a spectrometer according toanother exemplary embodiment. The spectrometer 200 illustrated in FIG. 2may include a single input coupler 111 and a single output coupler 114.The input coupler 111 and output coupler 114 may be optically connectedto at least two waveguides 112 and at least two resonators 113. Otherthan the number of the input coupler 111 and the output coupler 114, theconfiguration of the spectrometer 200 illustrated in FIG. 2 may beidentical to the configuration of the spectrometer 100 illustrated inFIG. 1. In the exemplary embodiment illustrated in FIG. 2, the inputcoupler 111 and the output coupler 114 may not have a wavelengthselectivity. For example, the input coupler 111 may couple lights of allwavelength bands and provide the coupled lights to waveguides 112respectively. Also, the resonators 113 having different resonancewavelengths respectively may output only the lights of the respectivewavelengths to the output coupler 114.

Also, although FIG. 2 illustrates that the spectrometer 200 includes oneinput coupler 111 and one output coupler 114, at least two inputcouplers 111 having a wavelength selectivity and one output coupler 114not having a wavelength selectivity may be included according to anotherexemplary embodiment. Also, one input coupler 111 not having awavelength selectivity and at least two output couplers 114 having awavelength selectivity may be included according to another exemplaryembodiment.

In general, the input coupler 111 includes a grating-type coupler havinga periodic grating structure, and the grating-type coupler has apolarization selectivity. For example, the input coupler 111 may coupleeither a p-polarization component (also referred to astransverse-magnetic (TM) component) or an s-polarization component (alsoreferred to as transverse-electric (TE) component) of light incidentonto the input coupler 111. When some polarization components of theincident light are not coupled, the coupling efficiency of the inputcoupler 11 may degrade and light loss may occur. In that case, stablespectrum analysis of the spectrometer may be difficult. The couplerdevice 140 according to the present exemplary embodiment may beconfigured to have a two-layer structure having a selectivity withrespect to the p-polarization component and the s-polarization componentto improve the coupling efficiency by coupling the lights of allpolarization components.

For example, FIG. 3 is a schematic cross-sectional view of a couplerdevice according to an exemplary embodiment. Referring to FIG. 3, thecoupler device 140 may include a first coupler layer 110 a and a secondcoupler layer 110 b. Also, the coupler device 140 may further include atransparent dielectric layer 101 in which the first coupler layer 110 aand the second coupler layer 110 b are buried. The first coupler layer110 a and the second coupler layer 110 b may be fixed and disposedrespectively in different layers by the transparent dielectric layer101. Herein, the first coupler layer 110 a and the second coupler layer110 b may include a material having a higher refractive index than thetransparent dielectric layer 101 therearound. For example, thetransparent dielectric layer 101 may include SiO₂ or siloxane-basedspin-on glass (SOG), and the first coupler layer 110 a and the secondcoupler layer 110 b may include a high-refractive index material such asTiO₂, SiN₃, ZnS, ZnSe, or Si₃N₄. Also, the first coupler layer 110 a andthe second coupler layer 110 b may include the same material or mayinclude different materials to improve the wavelength selectivity.

As illustrated in FIG. 3, the first coupler layer 110 a and the secondcoupler layer 110 b may be disposed respectively in different layersalong an incident light propagation direction in the transparentdielectric layer 101. The first coupler layer 110 a and the secondcoupler layer 110 b may have opposite polarization selectivities. Forexample, the first coupler layer 110 a may be configured to have aselectivity with respect to the light of the p-polarization component,and the second coupler layer 110 b may be configured to have aselectivity with respect to the light of the s-polarization component.In this regard, the coupler device 140 may be a dual coupler devicehaving a dual-layer structure.

The first coupler layer 110 a may include a first input coupler 111 a, afirst waveguide 112 a, a first resonator 113 a, and a first outputcoupler 114 a that are disposed in the same layer. Although notillustrated in FIG. 3, as illustrated in FIGS. 1 and 2, the firstcoupler layer 110 a may include at least two first input couplers 111 a,at least two first waveguides 112 a, at least two first resonators 113a, and at least two first output couplers 114 a, which have differentwavelength selectivities. Also, each of the first resonators 113 a mayinclude two resonator mirrors 121 a and 122 a that are disposed in thefirst waveguide 112 a. Herein, the first input coupler 111 a may be, forexample, a grating-type coupler having a periodic grating structureconfigured to have a selectivity with respect to the light of thep-polarization component. Thus, the light of the p-polarizationcomponent among the incident lights may be provided to the firstwaveguide 112 a through the first input coupler 111 a.

Also, the second coupler layer 110 b may include a second input coupler111 b, a second waveguide 112 b, a second resonator 113 b, and a secondoutput coupler 114 b that are disposed in the same layer. Like the firstcoupler layer 110 a, the second coupler layer 110 b may include at leasttwo second input couplers 111 b, at least two second waveguides 112 b,at least two second resonators 113 b, and at least two second outputcouplers 114 b, which have different wavelength selectivities. Each ofthe second resonators 113 b may include two resonator mirrors 121 b and122 b that are disposed in the second waveguide 112 b. The second inputcoupler 111 b may be, for example, a grating-type coupler having aperiodic grating structure configured to have a selectivity with respectto the light of the s-polarization component. Thus, the light of thes-polarization component among the incident lights may be provided tothe second waveguide 112 b through the second input coupler 111 b.

The first coupler layer 110 a and the second coupler layer 110 b may bedisposed in different layers to be parallel to and face each other. Forexample, the first input coupler 111 a, the first waveguide 112 a, thefirst resonator 113 a, and the first output coupler 114 a of the firstcoupler layer 110 a may be arranged in parallel to the second inputcoupler 111 b, the second waveguide 112 b, the second resonator 113 b,and the second output coupler 114 b of the second coupler layer 110 b.Also, the at least two first input couplers 111 a, the at least twofirst waveguides 112 a, and the at least two first resonators 113 a ofthe first coupler layer 110 a arranged in the widthwise direction of thecoupler device 140 may be disposed to face the at least two second inputcouplers 111 b, the at least two second waveguides 112 b, and the atleast two second resonators 113 b of the second coupler layer 110 b,respectively. When two elements face each other, the two elements appearto overlap with each other when viewed in a height wise direction, thatis, the vertical direction of the top surface of the transparentdielectric layer 101.

The first and second input couplers 111 a and 111 b disposed to faceeach other may be configured to have different polarizationselectivities with respect to the same wavelength band. For example, thefirst input coupler 111 a configured to selectively couple the light ofthe first wavelength band λ1 having the p-polarization component may bedisposed to face the second input coupler 111 b configured toselectively couple the light of the first wavelength band λ1 having thes-polarization component. However, the wavelength bands of the lightscoupled respectively by the first input coupler 111 a and the secondinput coupler 111 b facing each other may not necessarily be identicalto each other. Instead, the wavelength band of the light coupled by thefirst input coupler 111 a may overlap partially with the wavelength bandof the light coupled by the second input coupler 111 b facing the firstinput coupler 111 a. For example, the wavelength band of the lightcoupled by the first input coupler 111 a may be λ1±Δλ, and thewavelength band of the light coupled by the second input coupler 111 bfacing the first input coupler 111 a may be λ1±Δλ′.

Likewise, the first and second resonators 113 a and 113 b disposed toface each other may be configured to have substantially the sameresonance wavelength. For example, the first resonator 113 a configuredto resonate the light of the first wavelength band λ1 may be disposed toface the second resonator 113 b configured to resonate the light of thefirst wavelength band λ1. The distance between the two resonator mirrors121 a and 122 a and the distance between the two resonator mirrors 121 band 122 b in the first and second resonators 113 a and 113 b disposed toface each other may be equal to each other.

As illustrated in FIG. 3, the first and second output couplers 114 a and114 b may be disposed respectively at positions that do not overlap witheach other in a lengthwise direction, that is, the light propagationdirection in the first and second waveguides 112 a and 112 b. This isdone so that the light output from the first output coupler 114 a andpropagating toward the photodetector 150 may not pass through the secondoutput coupler 114 b. Thus, the light propagating from the first outputcoupler 114 a toward the photodetector 150 may reach the photodetector150 without being obstructed by the second output coupler 114 b.

Although it has been described above that at least two first inputcouplers 111 a, at least two second input couplers 111 b, at least twofirst output couplers 114 a, and at least two second output couplers 114b are disposed, the coupler device 140 illustrated in FIG. 3 may beapplied to the spectrometer 100 illustrated in FIG. 1 and also to thespectrometer 200 illustrated in FIG. 2. For example, only one firstinput coupler 111 a may be optically connected to the at least two firstwaveguides 112 a and the at least two first resonators 113 a. Also, onlyone second input coupler 111 b may be optically connected to the atleast two second waveguides 112 b and the at least two second resonators113 b.

The coupling efficiency of the coupler device 140 may be improved byusing the first coupler layer 110 a and the second coupler layer 110 boperating independently of each other as described above. For example,the first coupler layer 110 a may be designed to optimize the receptionof the light of the p-polarization component, and the second couplerlayer 110 b may be designed to optimize the reception of the light ofthe s-polarization component. Thus, the coupler device 140 may receiveboth the light of the p-polarization component and the light of thes-polarization component, which are included in the incident lights,with high efficiency. Consequently, the spectrum analysis accuracy ofthe spectrometers 100 and 200 including the coupler device 140 may beimproved. Also, the first coupler layer 110 a and the second couplerlayer 110 b may be arranged in different-height layers withoutincreasing the area of the coupler device 140. Thus, the spectrometers100 and 200 including the coupler device 140 may be miniaturized.

FIG. 4 is a schematic cross-sectional view of a coupler device accordingto another exemplary embodiment. As shown in FIG. 4, the coupler device140 may further include a first reflector 131 and a second reflector132. The first reflector 131 may be disposed to face the first andsecond input couplers 111 a and 111 b, and the second reflector 132 maybe disposed to face the first and second output couplers 114 a and 114b.

The first reflector 131 is configured to reflect light, which passesthrough the first and second input couplers 111 a and 111 b withoutbeing absorbed by the first and second input couplers 111 a and 111 b,to the first and second input couplers 111 a and 111 b. When light isprojected onto the first and second input couplers 111 a and 111 b, someof the light passes through the first and second input couplers 111 aand 111 b without being absorbed and reaches the first reflector 131.The light incident on the first reflector 131 may bounce back in thedirection it comes from. The first and second input couplers 111 a and111 b may receive the light bouncing off the first reflector 131. Thus,the coupling efficiency of the coupler device 140 may be furtherimproved by reusing the light that remains without being absorbed. Thefirst reflector 131 may be disposed on an opposite side to a lightincident surface of the coupler device 140 on which the light isincident. For example, when the light is incident on the top surface ofthe coupler device 140, the first reflector 131 may be disposed betweenthe bottom surface of the coupler device 140 and the second inputcoupler 111 b.

In particular, the coupling efficiency of the first and second inputcouplers 111 a and 111 b may be further improved by using the fact thata phase difference occurs between the reflected light of thep-polarization component and the reflected light of the s-polarizationcomponent when the light is incident on the first reflector 131 at anangle smaller than the Brewster's angle. In general, when the firstreflector 131 is a perfect conductor, the phase difference between thereflected light of the p-polarization component and the reflected lightof the s-polarization component is 180°, and the same effect may beachieved also in a dielectric Bragg reflector. Thus, the distancebetween the first input coupler 111 a and the first reflector 131 may beset to cause a destructive interference between the incident light andthe reflected light with respect to the light of the s-polarizationcomponent and a constructive interference between the incident light andthe reflected light with respect to the light of the p-polarizationcomponent in the first input coupler 111 a. Then, the selectivity of thelight of the p-polarization component in the first input coupler 111 amay be further improved. Also, the distance between the second inputcoupler 111 b and the first reflector 131 may be set to cause adestructive interference between the incident light and the reflectedlight with respect to the light of the p-polarization component and aconstructive interference between the incident light and the reflectedlight with respect to the light of the s-polarization component in thesecond input coupler 111 b. Then, the selectivity of the light of thes-polarization component in the second input coupler 111 b may befurther improved.

For example, a finite-difference in time-domain (FDTD) simulation isperformed to verify the effect of the spectrometer 100 illustrated inFIG. 1. In the FDTD simulation, it is assumed that a grating pitch sizeof the input coupler 111 is 600˜700 nm, the waveguide 112 is formed ofSi₃N₄, the transparent dielectric layer 101 is formed of SiO₂, adistance between the first coupler layer 110 a and the second couplerlayer 110 b is 2.2 um, and a distance between the second coupler layer110 b and the first reflector 131 is 540 nm. As a result of the FDTDsimulation, when the first reflector 131 is not disposed, about 25% ofthe light of the p-polarization component is absorbed by the first inputcoupler 111 a and about 6% of the light of the p-polarization componentis absorbed by the second input coupler 111 b. Also, about 4% of thelight of the s-polarization component is absorbed by the first inputcoupler 111 a and about 11% of the light of the s-polarization componentis absorbed by the second input coupler 111 b. On the other hand, whenthe first reflector 131 is disposed, about 60% of the light of thep-polarization component is absorbed by the first input coupler 111 aand about 1% of the light of the p-polarization component is absorbed bythe second input coupler 111 b. Also, about 2% of the light of thes-polarization component is absorbed by the first input coupler 111 aand about 50% of the light of the s-polarization component is absorbedby the second input coupler 111 b. Thus, the signal-to-noise ratio andthe coupling efficiency of the coupler device 140 may be greatlyimproved.

Also, the second reflector 132 is configured to reflect the light, whichis scattered without propagating from the first and second outputcouplers 114 a and 114 b, to the photodetector 150. The output couplingefficiency may be improved by increasing the amount of light output tothe photodetector 150 by using the second reflector 132. The secondreflector 132 may be disposed on an opposite side to the photodetector150. For example, when the photodetector 150 is disposed to face thebottom surface of the coupler device 140, the second reflector 132 maybe disposed between the top surface of the coupler device 140 and thefirst input coupler 111 a.

The spectrometers 100 and 200 may be manufactured to be micro-sized inthe form of a semiconductor chip while having high resolution andaccuracy. Thus, a non-invasive biometric sensor installed in a mobileapparatus may be implemented by using the above spectrometers 100 and200.

For example, FIG. 5 is a schematic block diagram of a non-invasivebiometric sensor including the spectrometer of FIG. 1 according to anexemplary embodiment. Referring to FIG. 5, the non-invasive biometricsensor 1000 may include a light source unit (e.g., light emitter) 300configured to radiate an excitation light LE to an object OBJ, and aspectrometer 100 configured to spectroscope a scattered light LSgenerated from the object OBJ. Herein, the object OBJ may include ahuman body, a living body of an animal, or a food. For example, theobject OBJ may be a human body for blood sugar measurement or a food forfreshness measurement, and may be a sample for analysis of air pollutionor water pollution.

The light source unit 300 may include a light source and may alsoinclude at least one optical member for guiding the light from the lightsource to a desired position of the object OBJ. The light source may beconfigured to radiate a light of a wavelength band predetermined basedon an analysis target property of the object OBJ. For example, the lightsource may radiate a near-infrared light of a wavelength band of about0.8 μm to about 2.5 μm. The light source may include, for example, alight-emitting diode (LED) or a laser diode (LD).

Also, the non-invasive biometric sensor 1000 may further include acontrol unit (e.g., a controller or hardware computing device) 600configured to analyze the properties of the object OBJ on the basis ofsignals sensed by the spectrometer 100 and generate correspondingcontrol signals. The control unit 600 may include a user interface 500and a signal processing unit (e.g., signal processor) 400. The userinterface unit 500 may include an input unit and a display. The signalprocessing unit 400 may analyze the properties of the object OBJ on thebasis of the signals sensed by the spectrometer 100. For example, thesignal processing unit 400 may analyze the properties of the object OBJby Raman spectroscopy or near-infrared (NIR) absorption spectrumanalysis. The Raman spectroscopy may use scattering (particularlyinelastic scattering) in which the light input into the object OBJ isscattered in various directions by colliding with molecules or atomsincluded in the object OBJ. In the inelastic scattering, instead ofbeing simply reflected from the surface of molecules or atoms, theincident light is emitted after being absorbed into molecules or atoms,wherein the scattered light may have a longer wavelength than theincident light and a wavelength difference between the scattered lightand the incident light may be about 200 nm or less. Various properties,such as the structure of molecules and the vibration of molecules in theobject OBJ, may be detected by analyzing the spectrum of the scatteredlight.

The signal processing unit 400 may process the analysis result into avideo signal to be displayed on the display of the user interface 500.Also, the signal processing unit 400 may transmit a control signal tothe light source unit 300 according to the input from the user interface500. For example, the signal processing unit 400 may be implemented by amicroprocessor.

The spectrometer 100 and the control unit 600 may be connected to eachother via wire or wireless communication. For example, the non-invasivebiometric sensor 1000 may be implemented as a mini portable device inwhich the spectrometer 100 and the control unit 600 are connected bywire. As another example, the control unit 600 may be mounted on aportable mobile communication device to wirelessly communicate with thespectrometer 100.

FIG. 6 illustrates an example of an optical arrangement of thenon-invasive biometric sensor 1000 illustrated in FIG. 5. Referring toFIG. 6, the non-invasive biometric sensor 1000 may be implemented as areflection type. An optical system of the non-invasive biometric sensor1000 may be configured such that the spectrometer 100 may sense thescattered light LS reflected from the object OBJ. For example, the lightsource unit 300 may include a light source 310, a light path converter320, and a diaphragm 330. Although the light path converter 320 isillustrated as being a prism type, this is merely exemplary and thelight path converter 320 may also be a beam splitter type or a flatmirror type. The light path converter 320 may be omitted according tothe position of the light source 310. Also, the light source unit 300may further include an optical lens 350 configured to focus thescattered light LS from the object OBJ on the spectrometer 100.

The excitation light LE radiated from the light source 310 collides witha molecular structure in the object OBJ. In turn, the excitation lightis absorbed into the molecular structure and emitted therefrom so that awavelength-converted scattered light LS is output from the object OBJ.The scattered light LS, that is, a biometric optical signal may includevarious spectrums having different wavelength conversion degreesaccording to the molecular states in the object OBJ. The non-invasivebiometric sensor 1000 includes an optical system structure in which thescattered light LS output along the same path as the input path of theexcitation light LE to the object OBJ is input to the spectrometer 100.Also, the non-invasive biometric sensor 1000 may further include anadditional optical device that branches the scattered light LS to thespectrometer 100.

FIG. 7 illustrates another example of the optical arrangement of thenon-invasive biometric sensor 1000 illustrated in FIG. 5. Referring toFIG. 7, the non-invasive biometric sensor 1000 may be implemented as atransmission type. An optical system of the non-invasive biometricsensor 1000 may be configured such that the spectrometer 100 may sensethe scattered light LS transmitted through the object OBJ. For example,the light source unit 300 may include a light source 310, a light pathconverter 320, and a diaphragm 330. Although the light path converter320 is illustrated as being a prism type, this is merely exemplary andthe light path converter 320 may also be a beam splitter type or a flatmirror type. The light path converter 320 may be omitted according tothe position of the light source 310. The light source unit 300 mayfurther include an optical lens 350 configured to focus the scatteredlight LS from the object OBJ on the spectrometer 100.

The excitation light LE radiated from the light source 310 collides witha molecular structure in the object OBJ. In turn, the excitation lightLE is absorbed into the molecular structure and emitted therefrom sothat a wavelength-converted scattered light LS is output from the objectOBJ. The scattered light LS, that is, a biometric optical signal mayinclude various spectrums having different wavelength conversion degreesaccording to the molecular states in the object OBJ. The non-invasivebiometric sensor 1000 includes an optical system structure in which thescattered light LS output through the object OBJ is input to thespectrometer 100.

FIG. 8 illustrates another example of the optical arrangement of thenon-invasive biometric sensor 1000 illustrated in FIG. 5. Referring toFIG. 8, the non-invasive biometric sensor 1000 may further include abase 380, and the light source 310 and the spectrometer 100 may bedisposed on the same surface of the base 380 or on different surfaces ofthe base 380. For example, the base 380 may be formed of a transparentmaterial, and the light source 310 and the spectrometer 100 may bedisposed on the same surface of the base 380 while being spaced apartfrom each other. In this case, the light source 310 may be disposed toradiate the excitation light LE to the object OBJ through the base 380.The spectrometer 100 may be disposed to sense the scattered light LSthat is input from the object OBJ through the base 380. Also, on theother surface of the base 380, an optical lens 360 may be furtherdisposed to focus the excitation light LE from the light source 310 onthe object OBJ and focus the scattered light LS from the object OBJ onthe spectrometer 100.

The base 380 may be formed of a flexible material. In this case, thenon-invasive biometric sensor 1000 may be configured to be wearable onthe object OBJ. For example, the non-invasive biometric sensor 1000 maybe implemented as an armlet-type non-invasive blood sugar sensor. Inthis case, the control unit 600 may be disposed on the base 380 togetherwith the spectrometer 100. As another example, the non-invasivebiometric sensor 1000 may be implemented in such a manner that only thelight source 310 and the spectrometer 100 are formed in an armlet-typewearable structure and the control unit 600 is mounted on a mobiledevice.

The foregoing exemplary embodiments are merely exemplary and are not tobe construed as limiting. The present teaching can be readily applied toother types of apparatuses. Also, the description of the exemplaryembodiments is intended to be illustrative, and not to limit the scopeof the claims, and many alternatives, modifications, and variations willbe apparent to those skilled in the art.

What is claimed is:
 1. A dual coupler device comprising: a first couplerlayer configured to receive a light of a first polarization componentamong incident lights; a second coupler layer configured to receive alight of a second polarization component among the incident lights; anda first reflector and a second reflector that are disposed apart fromthe first coupler layer and the second coupler layer, and configured toreflect light, which is incident onto the first reflector and the secondreflector, respectively, after passing through the first coupler layerand the second coupler layer, wherein the first coupler layer isdisposed between the second reflector and the second coupler layer, andthe second coupler layer is disposed between the first reflector and thefirst coupler layer, wherein the first coupler layer and the secondcoupler layer have opposite polarization selectivities, and apolarization direction of the light of the first polarization componentis perpendicular to a polarization direction of the light of the secondpolarization component, and wherein the first coupler layer and thesecond coupler layer are spaced apart from each other in a verticaldirection and extended along a horizontal direction in which theincident lights propagate in the first coupler layer and the secondcoupler layer.
 2. The dual coupler device of claim 1, wherein the firstcoupler layer and the second coupler layer are parallel to and face eachother.
 3. The dual coupler device of claim 1, further comprising atransparent dielectric layer in which the first coupler layer and thesecond coupler layer are buried, wherein the first coupler layer and thesecond coupler layer have a refractive index that is higher than arefractive index of the transparent dielectric layer.
 4. The dualcoupler device of claim 1, wherein each of the first coupler layer andthe second coupler layer comprises a grating-type coupler having aperiodic grating structure.
 5. The dual coupler device of claim 4,wherein the periodic grating structure of the first coupler layer isconfigured to have a first polarization selectivity with respect to thelight of the first polarization component, and the periodic gratingstructure of the second coupler layer is configured to have a secondpolarization selectivity with respect to the light of the secondpolarization component.
 6. The dual coupler device of claim 4, whereinthe periodic grating structure of the first coupler layer is configuredto have a first wavelength selectivity with respect to a light of afirst wavelength band, and the periodic grating structure of the secondcoupler layer is configured to have a second wavelength selectivity withrespect to a light of a second wavelength band that overlaps at leastpartially with the first wavelength band.
 7. The dual coupler device ofclaim 6, wherein the first wavelength band and the second wavelengthband are substantially identical to each other.
 8. The dual couplerdevice of claim 1, wherein the first reflector is disposed apart fromthe first coupler layer by a first distance that creates, in the firstcoupler layer, destructive interference between the light of the secondpolarization component and the reflected light and constructiveinterference between the light of the first polarization component andthe reflected light, and wherein the second reflector is disposed apartfrom the second coupler layer by a second distance that creates, in thesecond coupler layer, destructive interference between the light of thefirst polarization component and the reflected light and constructiveinterference between the light of the second polarization component andthe reflected light.
 9. A spectrometer comprising: a first coupler layerconfigured to receive a light of a first polarization component amongincident lights; a second coupler layer configured to receive a light ofa second polarization component among the incident lights; aphotodetector configured to detect the light received by each of thefirst coupler layer and the second coupler layer; and a first reflectorand a second reflector that are disposed apart from the first couplerlayer and the second coupler layer, and configured to reflect light,which is incident onto the first reflector and the second reflector,respectively, after passing through the first coupler layer and thesecond coupler layer, wherein the first coupler layer is disposedbetween the second reflector and the second coupler layer, and thesecond coupler layer is disposed between the first reflector and thefirst coupler layer, wherein the first coupler layer and the secondcoupler layer have opposite polarization selectivities, and apolarization direction of the light of the first polarization componentis perpendicular to a polarization direction of the light of the secondpolarization component, and wherein the first coupler layer and thesecond coupler layer are spaced apart from each other and extended alonga direction in which the incident lights propagate in the first couplerlayer and the second coupler layer.
 10. The spectrometer of claim 9,wherein the first coupler layer comprises: a first input couplerconfigured to selectively couple the light of the first polarizationcomponent; a first waveguide along which the light of the firstpolarization component coupled by the first input coupler propagates; afirst resonator configured to resonate the light of the firstpolarization component coupled by the first input coupler; and a firstoutput coupler configured to output the light of the first polarizationcomponent resonated by the first resonator to the photodetector, and thesecond coupler layer comprises: a second input coupler configured toselectively couple the light of the second polarization component; asecond waveguide along which the light of the second polarizationcomponent coupled by the second input coupler propagates; a secondresonator configured to resonate the light of the second polarizationcomponent coupled by the second input coupler; and a second outputcoupler configured to output the light of the second polarizationcomponent resonated by the second resonator to the photodetector. 11.The spectrometer of claim 10, wherein the first coupler layer comprisesat least two first resonators configured to resonate lights of differentwavelengths respectively, and the second coupler layer comprises atleast two second resonators configured to resonate lights of differentwavelengths respectively.
 12. The spectrometer of claim 11, wherein oneof the at least two first resonators of the first coupler layer and oneof the at least two second resonators of the second coupler layer areconfigured to resonate lights of substantially the same wavelength. 13.The spectrometer of claim 11, wherein the first coupler layer comprisesat least two first input couplers configured to selectively couplelights of different wavelengths respectively, and the second couplerlayer comprises at least two second input couplers configured toselectively couple lights of different wavelengths respectively.
 14. Thespectrometer of claim 11, wherein the first input coupler is opticallyconnected to the at least two first resonators, and the second inputcoupler is optically connected to the at least two second resonators.15. The spectrometer of claim 11, wherein the first coupler layercomprises at least two first waveguides optically connected to the atleast two first resonators respectively, and the second coupler layercomprises at least two second waveguides optically connected to the atleast two second resonators respectively.
 16. The spectrometer of claim10, wherein the first output coupler and the second output coupler aredisposed respectively at positions that do not overlap with each otherin a light propagation direction in the first waveguide and the secondwaveguide.
 17. The spectrometer of claim 10, wherein the first reflectoris disposed apart from the first coupler layer by a first distance thatcreates, in the first coupler layer, destructive interference betweenthe light of the second polarization component and the reflected light,and constructive interference between the light of the firstpolarization component and the reflected light, and wherein the secondreflector is disposed apart from the second coupler layer by a seconddistance that creates, in the second coupler layer, destructiveinterference between the light of the first polarization component andthe reflected light, and constructive interference between the light ofthe second polarization component and the reflected light.
 18. Thespectrometer of claim 10, wherein the light reflected from the secondreflector travels to the second coupler layer after passing through thefirst coupler layer and a gap between the first coupler layer and thesecond coupler layer, and wherein the fight reflected from the firstreflector travels to the first coupler layer after passing through thesecond coupler layer and the gap between the first coupler layer and thesecond coupler layer.
 19. A non-invasive biometric sensor comprising: alight source configured to radiate an excitation light to an object; anda spectrometer configured to measure a spectrum distribution of ascattered light generated from the object by the excitation light, thespectrometer comprising: a first coupler layer configured to receive alight of a first polarization component among incident lights; a secondcoupler layer configured to receive a light of a second polarizationcomponent among the incident lights; a photodetector configured todetect the light received by each of the first coupler layer and thesecond coupler layer; a first reflector and a second reflector that aredisposed apart from the first coupler layer and the second couplerlayer, and configured to reflect light, which is incident onto the firstreflector and the second reflector, respectively, after passing throughboth the first coupler layer and the second coupler layer, wherein thefirst coupler layer is disposed between the second reflector and thesecond coupler layer, and the second coupler layer is disposed betweenthe first reflector and the first coupler layer, wherein the firstcoupler layer and the second coupler layer have opposite polarizationselectivities, and a polarization direction of the light of the firstpolarization component is perpendicular to a polarization direction ofthe light of the second polarization component, and wherein the firstcoupler layer and the second coupler layer are spaced apart from eachother and extended along a direction in which the incident lightspropagate in the first coupler layer and the second coupler layer.
 20. Aspectrometer comprising: a first coupler layer configured to receivelight of a p-polarization component through a first input coupler; asecond coupler layer that is configured to receive light of ans-polarization component through a second input coupler and disposed tobe apart from the first coupler layer in a first direction perpendicularto a second direction in which the light of the p-polarization componentand the light of the s-polarization component propagate in the firstcoupler layer and the second coupler layer, respectively; and a firstreflector and a second reflector that are disposed to be apart from thefirst coupler layer and the second coupler layer, and configured tobounce off light, which is incident from the first input coupler and thesecond input coupler after passing through both the first input couplerand the second input coupler, back to the first input coupler and thesecond input coupler, wherein the first coupler layer is disposedbetween the second reflector and the second coupler layer, and thesecond coupler layer is disposed between the first reflector and thefirst coupler layer, and wherein the first coupler layer and the secondcoupler layer have opposite polarization selectivities.
 21. Thespectrometer of claim 20, wherein the first coupler layer propagates thelight of the p-polarization component towards a first output couplerdisposed on the first coupler layer, the second coupler layer propagatesthe light of the s-polarization component towards a second outputcoupler disposed on the second coupler layer, and the first outputcoupler is disposed out of alignment with the second output coupler inthe second direction.
 22. The spectrometer of claim 21, wherein thefirst coupler layer is disposed between the second reflector and thesecond coupler layer so that the light bounced off from the secondreflector travels to the second coupler layer after passing through thefirst coupler layer and a gap between the first coupler layer and thesecond coupler layer, and wherein the second coupler layer is disposedbetween the first reflector and the first coupler layer so that thelight bounced off from the second reflector travels to the secondcoupler layer after passing through the first coupler layer and the gapbetween the first coupler layer and the second coupler layer.